Diesel emissions control after-treatment systems and related method

ABSTRACT

A diesel emissions control system or diesel emissions control after- treatment (“DECAT”) system thermally stabilizes and catalyzes engine exhaust. The system generates substantial reduced volatile organic compounds (“VOCs”) and hydrocarbons (“HCs”), as well as selective catalytic reduction (“SCR”) of nitrogen oxides (“NOx”). The system treats exhaust gases rich in particulate matter (“PM”) prior to a downstream diesel particulate converter (“DPC”). The DPC agglomerates the PM into larger and heavier soot that may be more readily captured by a deep bed of composite wire mesh filters. The system includes a base metal catalyst with an iron-containing zeolite catalyst augmented with cerium-manganese oxide (the “IZCM Catalyst”).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/616,636, filed on Mar. 28, 2012. The disclosure of the above application is incorporated herein by reference in its entirety.

FIELD

The present teachings generally concern diesel emissions control after-treatment (“DECAT”) systems. More particularly, the present teachings concern a DECAT system incorporating a base metal catalyst. The present teachings also more particularly concern a method of controlling diesel emissions with a base metal catalyst.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Controlling pollution is a formidable task. This task is even more daunting in environments where relatively less sophisticated or “dirty” diesel engines burn fuels containing high levels of sulfur (350+ppm). So-called conventional DECAT systems designed for relatively clean diesel engines polluting Organization for Economic Co-operation and Development (“OECD”) countries are not suited for use with high sulfur level fuels because their diesel oxidation catalyst (“DOC”) and diesel particulate filter (“DPF”) embodiments contain precious metals, requiring ultra-low sulfur diesel (“ULSD”) fuel to prevent failures attributed to sulfur poisoning.

ULSD fuel availability is sparse outside countries in the OECD. That factor, along with the cost burdens of complex active DPF components needed to generate high exhaust temperatures for soot burning purposes, render conventional DECAT systems impracticable for most applications in less developed countries (“LDCs”). Emerging LDC economies are powered to a great extent by millions of dirty diesel engines, super-emitters of volatile organic compounds (“VOC”), hydrocarbons (“HC”), nitrogen oxides (“NOx”), particulate matter (“PM”) and other pollutants known to cause substantial local and cross-border health and environmental damage, as well as climate changes caused by their intense global warming potency. Therefore, LDCs need viable alternatives to conventional DECAT systems.

SUMMARY

It is another object of the present teachings to provide a hybrid DECAT apparatus that generates substantial reductions of volatile organic compounds and hydrocarbons, as well as selective catalytic reduction (“SCR”) of nitrogen oxides, prior to introduction of an exhaust stream into a downstream diesel particulate converter (“DPC”).

It is another object of the present teachings to provide a DECAT system that is (i) highly resistant to sulfur and HC poison, (ii) compatible for interaction with similarly cost effective DPC Systems predicated on exhaust cooling, and (iii) optimized for installations in less developed countries with emerging economies where millions of relatively inefficient diesel engines powered by fuels with high sulfur content are notorious super-emitters of PM, VOC, HC, NOx and other pollutants, spreading substantial local and cross-border health and environmental damage, as well as climate changes caused by their intense global warming potency.

In accordance with one particular aspect, the present teachings provide a diesel emissions control after-treatment system including a urea supply source and a DECAT device. The urea supply source is operative for injecting a reductant into an exhaust stream. The DECAT device receives the exhaust stream containing the reductant. The DECAT device includes a thermal stabilizer section and a catalyst section. The thermal stabilizer section is operative to reduce a temperature of the exhaust stream to 350° C. or less. The catalyst section includes a base metal catalyst with an iron-containing zeolite catalyst augmented with cerium-manganese oxide (“IZCM catalyst”).

In accordance with another particular aspect, the present teachings provide a method of treating diesel exhaust including injecting a reductant from a urea supply source into an exhaust stream. The method additionally includes treating the exhaust stream containing the reductant with a thermal stabilizer section of a DECAT device, the thermal stabilizer section operative to reduce a temperature of the exhaust stream to 350° C. or less. The method further includes treating the exhaust stream containing the reductant with a catalyst section of the DECAT device, the catalyst section including a base metal catalyst with an iron-containing zeolite catalyst augmented with cerium-manganese oxide (“IZCM catalyst”).

DRAWINGS

The present teachings will become more fully understood from the detailed description, the following drawing(s) and any appended claims.

FIG. 1 is block diagram illustrating a DECAT system in accordance with the present teachings, the system shown operatively interacting with diesel exhaust, exhaust cooling embodiment(s) and a diesel particulate converter;

FIG. 2 is a schematic illustration of a DECAT device in accordance with the teachings of the present disclosure; and

FIG. 3 is a schematic illustration of another DECAT device in accordance with the teachings of the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. The description and any specific examples, while indicating embodiments of the present disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

With general reference to the block diagram of FIG. 1, a DECAT system in accordance with the present teachings is described. The present system is shown operatively associated with a diesel engine 1. In so far as the present teachings are concerned, it is understood that the diesel engine 1 is conventional in operation and constructions. In this regard, the diesel engine produces a baseline diesel exhaust or exhaust gases 2. The exhaust gases are rich in PM, as well as VOC, HC and NOx.

In one particular application, the diesel engine 1 is a mobile diesel engine. For example, the diesel engine may power a vehicle or a ship. It is understood, however, that the present teachings are not so limited. In this regard, the diesel engine may be incorporated into a stationary power plant.

The diesel engine 1 emits a raw diesel exhaust stream. In addition to VOC, HC and PM, diesel exhaust streams typically contain a considerable amount of NOx. The exhaust gases 2 initially pass through one or more cooling devices 3. Various cooling devices known in the art may be employed within the scope of the present teachings. For example, U.S. Pat. Nos. 7,266,943 and 7,976,801 describe exemplary cooling devices 3 suitable for use with the present teachings. Other cooling devices may be alternatively employed. The cooling devices 3 generally function to facilitate condensation of heavy and frequently toxic VOC fractions of PM into particles that may be captured at high frequencies and eliminated before exhaust leaves the tailpipe. U.S. Pat. Nos. 7,266,943 and 7,976,801 are hereby incorporated by reference as if fully set forth herein.

Simple passive DECAT systems taught by U.S. Pat. Nos. 7,266,943 and 7,976,801 are generally more suitable for LDCs because they are void of precious metals and complex active components, are sulfur resistant and therefore considerably more cost effective. Such simple passive DECAT systems inter alia employ (i) exhaust cooling embodiment(s)s to facilitate the condensation of heavy VOC fractions into PM that can be captured at high frequencies and (ii) DPCs with composite wire mesh filters to agglomerate PM into larger heavier soot dendrites that are more readily extractable from exhaust streams.

Cooled exhaust gases 4 are injected with a reductant. As shown in FIG. 1, the reductant may be delivered from a supply source 5. The supply source 5 is located downstream from cooled exhaust 4 exiting the exhaust cooling devices 3.

The reductant may be an ammonia source. In one particular application, the reductant is urea. It is appreciated by those skilled in the art, however, that other reductants may be used within the scope of the present teachings. Depending on the type of reductant employed and the exhaust gas temperatures, the reductant may be introduced at various points.

The cooled exhaust 4 progresses downstream and enters a hybrid DECAT device 12 of the present teachings. The cooled exhaust 4 first travels through a thermal stabilizer section 6 of the hybrid DECAT device 12 (FIGS. 2 and 3). The thermal stabilizer section 6 may be comprised of a wire mesh media having high thermal conductivity, high thermal inertia and high permeability. The composition of the wire mesh media may include a wire mesh matrix. It is appreciated by those skilled in the art, however, that the wire mesh media may be alternatively constructed.

The thermal stabilizer section 6 of the hybrid DECAT device 12 functions to further reduce the temperature of the exhaust stream. Accordingly to various embodiments, the thermal stabilizer section 6 may operate to reduce the temperature of the exhaust stream to approximately 350° C. or less. The exhaust stream may be maintained thereafter in a range of approximately to 250° C. to approximately 350° C.

In various embodiments, and as illustrated in FIG. 1, the reductant may be introduced into the stream of cooled exhaust 4 after the thermal stabilizer section 6. In this regard, the reductant may be injected into the exhaust stream between the thermal stabilizer section 6 and an IZCM catalyst section 7 (discussed further below). This embodiment may be preferred where exhaust is still relatively hot (over 350° C.), which may cause the cerium-manganese oxide catalyst to become so active that it may oxidize the ammonia source with the nitric oxide, thus eliminating the reductant needed for NOx conversion to N₂ and H₂O. Thus, the added cooling impact of the thermal stabilizer section 6 helps reduce that potential occurrence.

After the exhaust stream is treated by the thermal stabilizer section 6 of the hybrid DECAT device 12, the exhaust stream enters ab IZCM catalyst section 7. The IZCM catalyst section 7 includes a base metal catalyst with an iron-containing zeolite catalyst augmented with cerium-manganese oxide. With the IZCM catalyst section 7, the exhaust stream is exposed to the iron and cerium-manganese oxide. As a result, substantial reductions of VOC and HC are achieved. Further, NOx is selectively catalytically reduced prior to further downstream migration of the exhaust stream.

The hybrid DECAT device 12 of the present disclosure employs base metals rather than precious metals and is thus sulfur resistant, making the device 12 compatible for interaction with DPC systems taught by U.S. Pat. Nos. 7,266,943 and 7,976,801, and therefore optimized for joint retrofit installations aimed at remediating dirty diesel pollution in LDCs.

The exhaust stream next enters a DPC 9. The DPC 9 functions to agglomerate the PM of the exhaust stream into larger and heavier soot that may be more readily extracted from the exhaust stream. The soot may be captured with a portion eliminated by NO₂ oxidation while it is allowed to reside for a period of time in a deep bed of composite wire mesh filters with retaining screens that may be positioned along their perimeter. In addition, the additional residence time created by the deep bed of composite wire mesh filters may result in extended SCR of NOx. Various methods may be used for the agglomeration and capture of PM from the exhaust stream with the teachings of the present invention. Suitable methods are described in U.S. Pat. No. 7,976,801 which was incorporated by reference above.

Clean exhaust 10 may exit from the DPC. The clean exhaust may be substantially void of VOC, HC, NOx and PM.

Rather than being burned, as in the case of a conventional DPF, captured agglomerated diesel soot (“CADS”) in a DPC can be disposed of by one of several methods. First, CADS can be collected via reverse pulsation of the DPC and then recycled by eco-friendly thermo-chemical conversion (“TCC”) processes into valuable solids, liquid fuels and gases, as taught in U.S. Provisional Ser. No. 61/531,126. Alternatively, CADS can be disposed of via electric incineration taking place along the outer perimeter of wire mesh DPC filters, a process that converts soot into harmless ash and steam, as disclosed in U.S. Pat. No. 7,976,801. Under either method, substantial reductions of PM are achieved. In yet another method of disposition, whereby a conventional DOC is also employed, soot nested inside a DPC's deep bed of wire mesh filters may also be eliminated via NO₂ oxidation, as discussed more fully below.

End stage captured agglomerated diesel soot (CADS) 11 may be collected for disposition. The CADS 11 may be disposed by pulsation of the

DPC for CADS collection and recycling by way of TCC processes. Such processes are addressed in U.S. Provisional Ser. No. 61/531,126, which is hereby incorporated by reference as if fully set forth herein. Alternatively, the CADS may be electrically incinerated, thereby converting the CADS into harmless ash and steam as taught by U.S. Pat. No. 7,976,801.

With additional reference to the schematic view of FIG. 2, the hybrid DECAT device 12 of the present teachings may include a single housing 13 with the thermal stabilizer section 6 and the IZCM catalyst section 7. In other relatively high exhaust environments, where the thermal stabilizer section 6 and IZCM catalyst section 7 reside in one housing, it may be helpful to insert a conventional iron-containing zeolite catalyst in the thermal stabilizer section 6 to facilitate SCR before exhaust gases reach the IZCM catalyst section 7.

As shown in the schematic view of FIG. 3, it may be alternatively desirable to incorporate the thermal stabilizer section 6 and IZCM catalyst section 7 into separate housings 14, 15. In such alternative applications, it may be easier to address special issues that may be caused by the cumulative length of such a device. Where there are two separate housings 14, 15, the housings 14, 15 may be separated by piping. The reductant may be injected into the piping.

Accordingly, the present teachings provide a hybrid DECAT system that generates substantial reductions of VOC and HC, as well as SCR of NOx, prior to introduction of an exhaust stream into a downstream DPC. As a result, highly cost effective DECAT systems may be provided that are optimized for installations in less developed countries with emerging economies where millions of relatively inefficient diesel engines powered by fuels with high sulfur content are notorious super-emitters of PM, VOC, HC, NOx and other pollutants, spreading substantial local and cross-border health and environmental damage, as well as climate changes caused by their intense global warming potency.

The DECAT system of the present disclosure is designed to thermally stabilize and catalyze an exhaust stream and in the process generate substantial reductions of VOCs and HCs, as well as selective catalytic reduction of NOx, prior to the migration of gases rich in PM to a downstream DPC where said PM is agglomerated into larger heavier soot dendrites that are ripe for disposition by several methods noted below.

The present teachings provide a hybrid DECAT system in which baseline exhaust temperatures are lowered by one or more exhaust cooling devices, then maintained in a relatively narrow range by thermal stabilizer properties. The thermal stabilizer's properties are contained in an upstream section of the DECAT device, followed by a downstream section containing the IZCM catalyst.

While specific examples have been described in the specification and illustrated in the drawings, it is understood by those skilled in the art that various changes may be made and equivalence may be substituted for elements thereof without departing from the scope of the present teachings as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various examples may be expressly contemplated herein so that one skilled in the art would appreciate from the present teachings that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise above. Moreover, many modifications may be made to adapt a particular situation or material to the present teachings without departing from the essential scope thereof. Therefore, it may be intended that the present teachings not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode of presently contemplated for carrying out the present teachings but that the scope of the present disclosure will include any embodiments following within the foregoing description and any appended claims. 

What is claimed is:
 1. A diesel emissions control after-treatment (“DECAT”) system for treating exhaust prior to a diesel particulate converter, the system comprising: a supply source for injecting a reductant into an exhaust stream; and a DECAT device for receiving the exhaust stream containing the reductant, the DECAT device including a thermal stabilizer section and a catalyst section, the thermal stabilizer section operative to reduce a temperature of the exhaust stream to 350° C. or less, the catalyst section including a base metal catalyst with an iron-containing zeolite catalyst augmented with cerium-manganese oxide (“IZCM catalyst”).
 2. The diesel emissions control after-treatment system of claim 1, wherein the thermal stabilizer section and the catalyst section are arranged such that the exhaust stream containing the reductant is first treated by the thermal stabilizer section and subsequently treated by the catalyst section.
 3. The diesel emissions control after-treatment system of claim 1, wherein the thermal stabilizer section and the catalyst section are contained within a common housing.
 4. The diesel emissions control after-treatment system of claim 1, wherein the thermal stabilizer section and the catalyst section are contained within separate housings.
 5. The diesel emissions control after-treatment system of claim 1, wherein the exhaust stream may be maintained within a range of approximately 250° C. to 350° C.
 6. The diesel emissions control after-treatment system of claim 1, wherein the thermal stabilizer section includes a wire mesh media.
 7. The diesel emissions control after-treatment system of claim 1, wherein the catalyst section is operative to substantially reduce VOC and HC.
 8. The diesel emissions control after-treatment system of claim 7, further wherein NOx is selectively catalytically reduced.
 9. The diesel emissions control after-treatment system of claim 1, further comprising at least one cooling device for condensing VOC fractions of PM.
 10. The diesel emissions control after-treatment system of claim 1, in combination with the diesel particulate converter.
 11. The diesel emissions control after-treatment system of claim 1, wherein the cerium-manganese component of catalyst section is operative to substantially reduce VOC and HC.
 12. The diesel emissions control after-treatment system of claim 4, wherein the separate housings are connected by a piping.
 13. The diesel emissions control after-treatment system of claim 4, wherein the reductant is injected into the piping.
 14. The diesel emissions control after-treatment system of claim 1, wherein the reductant is an ammonia source.
 15. The diesel emissions control after-treatment system of claim 1, wherein the reductant is urea.
 16. The diesel emissions control after-treatment system of claim 3, wherein the reductant is after the thermal stabilizer section before the catalyst section.
 17. A method of treating diesel exhaust prior to a diesel particulate converter, the method comprising: injecting a reductant from a supply source into an exhaust stream; treating the exhaust stream containing the reductant with a thermal stabilizer section of a DECAT device, the thermal stabilizer section operative to reduce a temperature of the exhaust stream to 350° C. or less; and treating the exhaust stream containing the reductant with a catalyst section of the DECAT device, the catalyst section including a base metal catalyst with an iron-containing zeolite catalyst augmented with cerium-manganese oxide (“IZCM catalyst”).
 18. The method of claim 17, wherein the exhaust stream containing the reductant is first treated with the thermal stabilizer section and subsequently treated with the catalyst section.
 19. The method of claim 17, further comprising maintaining the exhaust stream within a range of approximately 250° C. to 350° C.
 20. The method of claim 17, wherein treating the exhaust stream containing the reductant with a catalyst section includes substantially reducing VOC and HC.
 21. The method of claim 17, wherein treating the exhaust stream containing the reductant with a catalyst section includes catalytically reducing NOx.
 22. The method of claim 17, further comprising condensing VOC fractions of PM with at least one cooling device.
 23. The method of claim 21, wherein condensing VOC fractions of PM with at least one cooling device occurs before injecting the reductant.
 24. The method of claim 17, wherein the reductant is injected after the thermal stabilizer section and before the catalyst section.
 25. The diesel emissions control after-treatment system of claim 1, further comprising an iron-containing zeolite catalyst in the thermal stabilizer section.
 26. The diesel emissions control after-treatment system of claim 25, wherein the iron-containing zeolite catalyst facilitates SCR caused by exposure of the reductant to the iron. 